1. Field of the Invention
The present invention relates to an image communication system, apparatus, and method for transmitting and receiving an image to and from remote sites over a digital communication line such as Integrated Service Digital Network (ISDN).
2. Related Background Art
With recent development of image compression and coding techniques as well as recent prevalence of high speed, high quality digital communication lines typically ISDN, various image communication systems have been developed which conform with Recommendations stipulated for audio video (AV) services such as television (TV) conference systems.
A TV conference system, a typical image communication system, is operated generally by preparing a TV conference room to have a conference with partners at a remote TV conference room. This conference is usually had by a plurality of participants in TV conference rooms in a multi-to-multi person style.
There are several methods of taking an image of a participant or participants in a TV conference room for the transmission of the image from its own TV conference terminal to a partner TV conference terminal. With one method, zooming of an image photographing unit (e.g., video camera) is set to a wide angle side to take the images of all participants, or with another method, a photographing unit with a tilting mechanism is used to take the image of a particular participant.
As one example of using the tilting mechanism of the photographing unit, a method has been proposed whereby a microphone is installed for each of all TV conference participants, the sound levels are checked, and the photographing unit is automatically moved toward the participant with the largest sound level. In most of TV conference systems, however, the tilting control of the photographing unit is performed by an operator who manipulates an operation console of the TV conference system.
Some image photographing units used by such a TV conference system can perform zooming control, focussing control as well as tilting control in the vertical and horizontal directions, in response to control information (command) supplied from the operation console. Further, some image photographing units have an automatic focussing function of automatically measuring a distance to an object and adjusting the focus of the object. Still further, some image photographing units have a plurality of range finding points on a photographing screen to adjust the focus of an arbitrary or particular object on the photographing screen.
In some TV conference systems and image photographing units having the same command system, the image photographing unit not only at the own side station but also at the partner side station can be controlled. In such TV conference systems, control information for the image photographing unit is transmitted to a TV conference terminal at the partner side station to control the image photographing unit at the partner side station.
In a TV conference system in which the image photographing unit is controlled by an operator who manipulates an operation console, for example, the direction of the image photographing unit is controlled by depressing tilt control keys (right, left, up, and down keys) of the image photographing unit. However, with this method, because the correspondence between the tilt direction of the image photographing unit and the tilt control key differs depending on the type of each TV conference system, the operator becomes confused in changing the photographing direction of the photographing unit at the own side station.
For example, consider the case where there are a window 100 (hereinafter called self-portrait display window) for displaying an image on the image display unit at the own side station and a window 101 (hereinafter called partner portrait display window) for displaying an image at a partner side station on the image display unit at the own side station. In this case, in order to move an object 103 displayed at the left of the partner portrait display window 101 to the center of the window 101, the photographing direction of the image photographing unit 105 at the partner side station (hereinafter called partner portrait photographing unit) is required to change to the direction indicated by an arrow 107. In this case, an operator usually depresses a "left key" of the tilt control keys.
On the other hand, in order to move an object 102 displayed at the left of the self-portrait display window 100 to the center of the window 100, the photographing direction of the image photographing unit 104 at the own side station (hereinafter called self-portrait photographing unit) is required to change to the direction indicated by an arrow 106.
Two types of manipulation by an operator of the tilt control keys may be had:
a) Depressing "left key", being coincident with the tilt direction as viewed from the self-portrait photographing unit 104, and PA1 b) Depressing "right key", being coincident with the tilt direction as views from the object 102.
In some TV conference systems, an operator can select either one of the two types, by setting the system to this effect.
As above, in a conventional TV conference system, because the correspondence between the tilt direction of the self-portrait photographing unit 104 and the tilt control key is different, the operator becomes confused in changing the photographing direction of the photographing unit.
Apart from the above, in controlling the partner portrait photographing unit 105 from the own side station, each time a key of the operation console at the TV conference terminal at the own side station is depressed, for example, each time the "left key" is depressed, a command such as "change the photographing direction of the partner portrait photographing unit 105) is transmitted over a communication line to the TV conference terminal at the partner side station. In response to this command, the photographing direction of the partner portrait photographing unit 105 is changed by an amount preset for this command. During or after this change, an image at the partner side station is transmitted over the communication line to the image display unit at the own side station, and displayed on the partner portrait display window 101.
After an operator depresses the control key for controlling the partner portrait photographing unit 105 at the TV conference terminal at the own side station, a new image reflecting this control is displayed on the partner portrait display window 101 at the own side station. During this period, there is a delay time in transferring a control command or image data and in coding and decoding an image. Therefore, an operator tends to depress the control key at the TV conference terminal at the own side station, more often than necessary, making difficult to change the direction of the partner portrait photographing unit 105 by a desired amount.
Such a problem occurs also in performing a zooming control of the partner portrait photographing unit 105 from the own side station. Specifically, after an operator depresses the zooming control key at the own side station, an image at the partner side station reflecting the control change is displayed on the partner portrait display window 101. During this period, there is a delay time so that it is difficult to zoom the image to a desired size.
Still further, if there are a plurality of participants in one TV conference room and a distance from the image photographing unit to each participant is different, it is necessary for a conventional TV conference system to manually adjust the focus, resulting in a complicated focus adjustment operation. Although an image photographing unit with an automatic focussing function is known, this unit automatically focusses to a participant located at the center of the display screen. Therefore, the participants other than the participant at the center of the display screen are out of focus and it is difficult to clearly discriminate between those participants.
Such a delay time is associated not only with the above-described controls but also, for example, with the case where an operator draws a desired image with a pointing device.